Answer: 3.
Step-by-step explanation: The answer is 3 because the original shape was a square with all of the sides with the length 5. Because there are 4 sides in a square, the perimeter of the square is 20(5+5+5+5). Now, the square has been reshaped into a rectangle. If one of the side lengths of the rectangle is 7, the opposite and parrallel side has to be 7. 7+7 is 14. Now the expression is perimeter = 14 + 2(missing width). If you plug in 3, that expression is now 14+6, which is 20. Therefore, the missing side width is 3.